1. Field of the Invention
The present invention relates to a passenger seat device of an automotive vehicle, the passenger seat device including a detector for detecting an occupant occupying a seat.
2. Description of Related Art
JP-A-2003-80989 proposes a passenger seat having a detector for detecting an occupant on the seat based on changes in an alternating electric field on and around the seat. This type of the occupant detector is referred to as a capacitance-type occupant detector. The occupant detector includes a first electrode embedded in the seat for forming an alternating electric field and a second electrode embedded in a seat-back for detecting changes in the electric field caused by an occupant seating on the seat. An impedance between the first and the second electrode becomes lower when a seat is occupied by a passenger because the passenger body is a dielectric member and a conductive member as well.
JP-A-2003-80989 also proposes to embed a seat heater heated by electric power underneath the detector electrode. A parasitic capacitor is formed between the detector electrode and the seat heater that is substantially at a constant potential. This parasitic capacitor gives an influence on an electric potential of the detector electrode. Sensitivity of the occupant detector is lowered when the large parasitic capacitor is equivalently coupled to the detector electrode. In addition, there is a problem that a heat resistance between a passenger on the seat and the seat heater is large because the seat heater is embedded at a lower portion of the seat to reduce an amount of the parasitic capacitor formed between the detector electrode and the seat heater.